Finishing Touches on the Lander

by Guy Beutelschies

Week of September 30, 1996

We finished our work on the lander. Experts came in and inspected
it to make sure that it was ready to be put inside the aeroshell. One
of the experts discovered that the latches that are used to hold the
petals tightly together during launch vibrations might not have enough
clearance to release smoothly on Mars under all circumstances. A couple
of days of schedule contingency were used to fix this problem.

On Sunday we had a project picnic. It was pouring down rain but we
had fun anyway.

Week of October 7

Finished fixing the petal latches. Next on the list was a broken wire
on the wind sensor. This science instrument uses extremely fine wires
to measure how fast the wind is blowing. A small amount of current is
run through the wires and the resulting voltage is measured. As the
wind blows, it cools the wires thus changing its resistance. The faster
the wind blows, the more the resistance changes. Somehow one of these
wires broke so a new one was soldered into place.

Had a basketball game with some visiting engineers. We crushed them
like bugs. It sure helps to have home court advantage!

Week of October 14

Installed the lander inside the aeroshell. The aeroshell is the container
that looks like the old Apollo entry vehicles (kind of like an upside-down
top). It has a heat shield on the bottom that uses the friction of the
Martian atmosphere to slow it down. Several tests were run to make sure
that everything works as expected in this configuration.

Put the aeroshell onto a spin table, a device that looks like a giant
record player. Because the spacecraft is spinning when it enters the
atmosphere, we have to make sure that it is balanced. If not, it would
wobble and possibly tumble out of control. The spin table whirls the
spacecraft around and provides data on how out-of-balance the craft
is. Aluminum weights are then attached at certain points inside the
aeroshell for balance. Access doors are installed to enable us to do
this.

Week of October 21

Mated the entry vehicle with the cruise stage. This section carries
all the equipment that we need to journey from Earth to Mars. It has
the solar array that provides power, small thrusters for steering and
attitude sensors. These sensors look at the sun and stars to tell us
where the spacecraft is pointed. One of the tests we performed was a
phasing test to make sure that when the sun or stars move past a sensor
from left to right, the software shows the same thing (and not right
to left). It's pretty easy to make a sign error so it is always good
to do an end-to-end test after everything is done.

We also did a test to make sure that when we command thruster 1 to
fire, thruster 1 actually fires and not some other thruster. To do this,
we filled the propellant tanks with nitrogen and listened for the gas
escape when the thruster valve opened. It is far too dangerous to actually
use rocket fuel and fire the thrusters inside the cleanroom.

Volleyball league started! This is six-person, co-ed indoor. There
are a lot of fun people on our team, mostly people who work at Kennedy
Space Center.

Week of October 28

Finished testing the cruise stage. Our next activity is to load rocket
fuel into the propulsion system. The fuel our spacecraft uses is hydrazine.
This is a very hazardous operation because if any fuel spills it could
start a fire. Hydrazine is extremely caustic and will burn your skin
if it touches you and is toxic to breathe. For these reasons, the crew
loading the fuel wears self-contained suits with air packs that look
like space suits.

I flew back to Los Angeles to sit on a review board for another JPL
project called Deep Space 1. The review was on how they planned to do
assembly, test and launch operations. I was brought in to explain how
Pathfinder worked and to give my opinion on their plans. It was fun
to see how another project does things. They even had bagels at the
review.